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Chem > Hydrocarbons > Flashcards

Hydrocarbons Flashcards

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1
Q

Alkanes

A

Very unreactive
Combust completely and incompletely
Free radical substitution reaction by chlorine or bromine

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2
Q

Free radical substitution

A

Three stages
Initiation
Propagation
Termination

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3
Q

Initiation

A

Homolytic fission of breaking of Cl-Cl covalent bond to form two Cl radicals

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4
Q

Propogation

A

Free Cl radicals attack alkanes to produce methyl radical as C-H bond breaks homolytically
Methyl radical can attack chlorine molecule forming chloromethane and regenerating Cl radical
These two propogation steps can go on and on as long as methyl and Cl still present

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5
Q

Termination

A

Eventually two free radicals collide with each other and a single molecule is formed
As no free radicals are made from this the chain reaction stops

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6
Q

Aliphatic hydrocarbons

A

Organised into chain

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7
Q

Aromatic hydrocarbons

A

Organised into benzene ring

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8
Q

Cracking

A

Used to obtain more useful alkanes and alkenes of lower Mr from larger hydrocarbon molecules
Long chain alkane—>shorter alkanes+alkenes

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9
Q

Alkenes

A

Much more reactive than alkanes

Unsaturated

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10
Q

Alkene plus Hydrogen

A

Alkane
Using nickel catalyst
Electrophilic addition reaction

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11
Q

Alkene plus steam

A

Alcohol
Using sulfuric or phosphoric acid catalyst
Electrophilic addition reaction

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12
Q

Alkene plus hydrogen halides

A

Haloalkane

Electrophilic addition reaction

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13
Q

Major product

A

Halogen atom bonded to the carbon with the least number of H attached

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14
Q

Minor product

A

Halogen atom bonded to the carbon with the most number of H attached

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15
Q

Alkene plus halogen

A

Dihaloalkane

Electrophilic addition reaction

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16
Q

Alkene plus cold, dilute, acidified manganate ions

A

Diol
Oxidation reaction
[O]

17
Q

Alkene plus hot, concentrated, acidified manganate ions

A

Products depend on what is bonded to the carbon atoms involved in the C=C bonds
C=C breaks completely
The OH group in the diol formed initially are further oxidised to ketones, aldehydes, carboxylic acids or carbon dioxide
Alkene with only hydrogens=CO2
Alkene with one alkyl group and a hydrogen=aldehyde which can then be further oxidised to a carboxylic acid
Alkene with two different alkyl groups=ketone

18
Q

Addition polymerisation

A

Alkene undergoes addition reaction with itself to form a longer polymer

19
Q

Electrophilic addition

A

Br approaches ethene and π bond repels electrons in Br-Br bond forcing an induced dipole
Eventually Br-Br bond breaks forming bonds between the carbon and bromine

20
Q

Polyalkenes

A

Chemically inert and biodegrade very slowly so can cause environmental problems
Can be burnt but need very high temperature to avoid poisonous combustion products being formed

21
Q

CO

A

Product of incomplete combustion of alkanes

Will bind to Hb so poses threat to humans

22
Q

Nitrogen in car engines

A

Will react with oxygen to produce oxides of nitrogen

These react with water in atmosphere to produce nitric acid which is a main cause of acid rain

23
Q

Unburnt hydrocarbons

A

Lead to serious health problems

Carcinogens

24
Q

Catalytic converters

A

Catalyse reactions in car engines using platinum
CO+NO—>CO2+1/2N2
CO+1/2O2—>CO2
Unburnt hydrocarbons+O2—>CO2+H2O
Even though catalytic converters remove poisonous pollutants, they can’t do anything for the greenhouse gas carbon dioxide being produced

25
Q

Air pollution cause by the combustion of fuel can be monitored by

A

Infra red spectroscopy

26
Q

describe the difference between sigma and pi bonds

A

sigma bonds = formed when an sp^2 orbital from each carbon overlap to form a single C-C bond
pi bonds = when two 2p orbitals overlap
both give rise to planar arrangement around C=C bonds

Chem (15 decks)

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